Electrical contact



- March 5, 1946.

-F. R. HENSEL ETAL 2,396,101

ELECTRICAL CONTACT Filed Oct. 23, 1942 ELECTRIC comer 0F REFRACTO RT 0x101:

OFBe Mi,C6.,Sr,orBa

0R GOLD INVENTORS FRANZ R. HENSEL y URL 1. LRRSEN PLUS .SILVER,COPPER Patented Mar. g, i946 umrse s'mrrs PATENT series ELECTRICAL CONTACT Franz R. Hensel and Earl I. Larsen, Indianapolis, Ind asslgnors to P. R. Mallory & 00., Inc., Indianapolis, Ind., a corporation of Delaware Application October 23, 1942, Serial No. 463,118

3 Claims. Cl. 200-166) This invention relates to electrical make and break contacts.

An object of the invention is to improve electric contacts. I

Another object of the invention is to improve electrical make and break contacts, and produce, due to the structural composition thereof, a reduced contact resistance, less tendency for arcing,

pitting, transferring or tendency to weld or fuse during operation, and which are less susceptible to tarnishing and oxidation, and operate in an improved manner as compared with electrical contacts commonly used in the same fields of application.

Other objects of the invention will be apparent from the description and claims.

Figure 1 is a plan view of an electrical termlna member embodying this invention; and

Figure 2 is a side "elevation of the structure of Figure 1.

Heretofore, electrical make and break contacts have been used in various applications, of which the use as contactor contacts in an electrical system may be taken as representative. Such contacts have been commonly made from various metals and alloys thereof, such as, for example, copper, silver, copper-tungsten mixtures, silvertungsten mixtures, and the like. Upon breaking an electrical circuit by separating two contact points, arcing occurs 'between these contacts,

which often gives rise to serious conditions materially affecting efiicient operation thereof. Under the action of the rapid recurrence of the arcing, the faces of the contacts pit, fuse and frequently transfer from one contact face to the other. Such deleterious effects are often accompanied by the formation of undesirable compounds which increase the contact resistance, the localization of the are, which increases the tendency to pit, stick and volatilize, and a building up of fused and spattered materials, on one or both of the contact faces, which often' results in complete failure of operation, due to a short circuiting.

In carrying out our present invention, a contact material is formed from an alley or mixture, containing a metal or an alloy, having a, relatively high electrical conductivity and a refractory oxide of one of the elements of the second group of the periodic table.

While we do not wish to be limited thereby, it is believed that the improved results obtained with the material of the present invention is due in part at least to the fact that the refractory oxide particles separate the contact metal particles, such as silver. The refractory oxide is not wetted by the silver or other metal and, hence, when an arc is drawn and a high temperature is reached the oxides prevent the flowing together of the silver to form a molten pool which would cause contact sticking. These oxides are very stable at high temperature and will not decom pose and form alloys at the temperature of contact arcing.

The relatively high electrical conducting metal may be copper, silver, gold or copper, silver or gold base alloys and an oxide of one of the alkaline earth metals, selected from the group consisting of beryllium, magnesium, calcium, strontium and barium.

The oxides of these metals are characterized by extremely high melting points, and a very high electrical resistivity. The oxides are furthermore very stable. The melting points of the principal oxides contemplated are as follows:

It can, therefore, be stated that the oxides which we intend to cover are characterized by a melting point exceeding 1800 C. The oxides are, for all practical purposes, non-conductors. The oxides are preferably used in proportions from 1 to 10%, with the balance of the contact composition formed of contact metal.

In addition to the straight oxides, the mixtures and compounds of oxides and silica may be used, such as kaolin which is an aluminum silicate. The following are examples of compositions produced in accordance with the present invention, which have shown very high resistance to welding or sticking, the respective proportions being given in the per cent by weight:

Beryllium oxide, 2%; silver, 98% Magnesium oxide, 5%; silver, 95% Calcium oxide, 3%; silver, 97% Barium oxide, 10%; silver, Beryllium oxide, 2%; copper, 98% Magnesium oxide, 5%; coppe Calcium oxide, 3%; owner, 97% Barium oxide, 10%; copper, 90%

The contact material may be formed by several different methods, for example:

(1) Finely divided particles of the relatively high electrical conductivity material are intimately mixed with finely divided particles of the oxide material. The mixed particles or powders materially reduced. The pressed piece may then be sintered in-asuitable atmosphere, so as to bring about a bonding or fritting of the metallic particles, to increase the strength of the contact.

After this sintering operation, the contact may be 7 re-pressed or hot workedor cold worked, to further increase the density, strength or other physical properties, after 'which it may again be sub- Jected to. a further sintering operation.

(2) Certain percentages of the relatively high 7 electrical conductivity material in' a finely divided state, may be mixed with certain percentages of the oxide material and pressed to form a somewhat relatively porous slug or bar, although, with the application of suflicient pressure, such slug or bar may be made to appear substantially'homogeneous to the naked eye. Such slugs or bars may have, however. as high as 40% of voids.

I The porous slug or bar is next filled with the impregnating material, which is of a character that imparts the desired characteristics. Metals whichare adapted to impart the characteristics may be copper or copper alloyao'r silver or silver alloys. To impregnate the aforementioned slugs or bars, with these materials, advantage i taken of the retentivity or capillary attraction of the voids or. pores in the bars or slugs for the impregnating material. To utilize this eifect, such materials must be liquified; to this end, the slugs or bars are placed in a suitable vessel, surrounded with sheets or bodies in other form, of the im- Pregnating material and heated to a temperature,

particles within the melt. The melt may then be cast into chill molds or cooled very rapidly so as tohold the oxide particles in suspension and accomplish the same result as cited in Example 1.

(4) The mixed refractory oxide and metal powders" may be hot pressed at a temperature] of the contact so as to act as a cementing agent.

One such material is sodium silicate.

While specific embodiments of the invention '7 have been described, it is-intended tocover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contact formed of 1 to 10% of refractory oxide selected from the group consisting of the oxides of beryllium, magnesium, calcium, strontium and barium and the balance substantially all contact metal selected from the group consisting of silver, copper and gold.

2. An electric contact formed of 1 to 10% of calcium oxide and the balance substantially all s1 ver.

3. An electrical contacting element subject to arcing comprising an electrically conductive metal composition formed of 1 to 10% of refractory insulating oxide material comprising'at least one of the oxides selected from the group consisting of oxides of beryllium, magnesium, calcium,

strontium and barium and the balance substantially all metal selected from the group consisting of silver, copper, and gold.

FRANZ R. HENSEL. EARL I. LARSEN.

not aisselve m the molten metal, butthe melt may be stirred vigorously, soas to bringjabout'a more or less? uniform distribution ot-the oxide 

